The present invention relates to an organic electroluminescence device (hereinafter, referred to as organic EL device) and a phenylenediamine derivative, and more particularly, an organic EL device comprising a pair of electrodes and an organic light emitting layer sandwiched in the electrodes, and a phenylenediamine derivative used as a material for the organic EL device and the like.
An organic EL device is being earnestly studied since it is a complete solid state device and can form a display and an illumination of light-weight and thin-form that is driven at a low voltage.
A problem on applying the organic EL device to a display is to make the driving voltage being a lower voltage. For example, by using a dendrimer of an aromatic amine disclosed in JP-A-4-308688 as a hole injection material, the driving voltage is lowered. The compound has a small ionization potential of 5.2 eV owing to the phenylenediamine skeleton, and exhibits an effect of lowering the driving voltage.
However, the compound having a phenylenediamine skeleton has a small hole mobility of 3xc3x9710xe2x88x925 cm2/Vxc2x7s, and therefore the driving voltage in the region of high electric current injection is insufficiently lowered.
A high molecular weight aromatic amine compound disclosed in JP-A-9-301934 has a small ionization potential of 5.2 eV but has a problem in that the hole mobility is insufficient. It is expected that the hole mobility be lowered due to the mixing of impurities.
That is, in the fluorescent spectrum of the compound disclosed in JP-A-9-301934 (FIG. 1), alight emission component having a maximum fluorescent wavelength peak of 500 nm or higher is observed, which is not present originally. This shows that impurities are mixed. Furthermore, the voltage is increased by 2.7 V with only driving time of 76 hours, which becomes a hindrance of lowering the driving voltage. Accordingly, in the device disclosed in the publication, the hole mobility is lowered and the driving voltage is increased by the impurities.
Furthermore, because it has a green fluorescent component, when the compound is used in the hole transporting zone of a blue light emitting device, blue light emission cannot be obtained due to mixing of green light emission component.
International Patent Publication WO98/30071 (published on Jul. 9, 1998) discloses an organic electroluminescence device using a compound similar to the present invention, but fails to disclose an effect in that a particular low voltage can be obtained on combining with a light emitting layer containing a charge injection auxiliary.
An object of the invention is to provide an organic EL device having a long life time that can decrease the driving voltage of the organic EL device.
Another object of the invention is to provide a material having a small ionization potential and exhibits a large hole mobility when it is used as a layer or a zone.
The invention is an organic electroluminescence device comprising a pair of electrodes and an organic light emitting layer sandwiched in the electrodes, characterized in that a hole transporting zone provided between the electrodes comprises a phenylenediamine derivative represented by the general formula (I), the general formula (II) or the general formula (II)xe2x80x2, the phenylenediamine derivative exhibits a hole mobility of at least 10xe2x88x924 cm2/Vxc2x7s on using as a layer or a zone, and the organic light emitting layer contains a charge injection auxiliary. 
(Ar1 to Ar6 represent an aryl group having from 6 to 24 nucleus carbon atoms, which may be substituted with a hydrogen atom, an alkyl or an alkoxy group having from 1 to 6 carbon atom(s), an aryl group having from 6 to 24 nucleus carbon atoms, or a styryl group. X represents a linking group, which is a single bond, arylene having from 6 to 24 nucleus carbon atoms, alkylene having from 1 to 6 carbon atom(s), diphenylmethylene, an ether bond, a thioether bond, a substituted or unsubstituted vinyl bond, or an aromatic heterocyclic ring. R1 and R2 represent an alkyl group having from 1 to 6 carbon atom(s), an alkoxy group, or a hydrogen atom, which may be bonded to each other to form a substituted or unsubstituted saturated 5-membered ring or a saturated 6-membered ring.) 
(Ar7 to Ar12 represent an aryl group having from 6 to 24 nucleus carbon atoms, which may be substituted with hydrogen atoms, an alkyl or an alkoxy group having from 1 to 6 carbon atom(s), an aryl group having from 6 to 24 nucleus carbon atoms, or a styryl group. Y represents a linking group, which is a single bond, arylene having from 6 to 24 nucleus carbon atoms, alkylene having from 1 to 6 carbon atom(s), diphenylmethylene, an ether bond, a thioether bond, an aromatic heterocyclic ring, or a substituted or unsubstituted vinyl bond. R3 and R4 represent an alkyl group having from 1 to 6 carbon atoms, an alkoxy group, or a hydrogen atom, which may be bonded to each other to form a substituted or unsubstituted saturated 5-membered ring or a saturated 6-membered ring.) 
(Ar7 to Ar12 represent an aryl group having from 6 to 24 nucleus carbon atoms, which may be substituted with a hydrogen atom, an alkyl or an alkoxy group having from 1 to 6 carbon atom(s), an aryl group having from 6 to 24 nucleus carbon atoms, or a styryl group. Y represents a linking group, which is a single bond, arylene having from 6 to 24 nucleus carbon atoms, alkylene having from 1 to 6 carbon atom(s), diphenylmethylene, an ether bond, a thioether bond, an aromatic heterocyclic ring, or a substituted or unsubstituted vinyl bond. R5 and R6 represent an alkyl group having from 1 to 6 carbon atom(s), an alkoxy group, or a hydrogen atom, which may be bonded to each other to form a substituted or unsubstituted saturated 5-membered ring or a saturated 6-membered ring.)
The hole transporting zone herein means a region of the organic EL device that has a function of transporting a hole from an anode. The function of transporting a hole is that it has a hole mobility of 10xe2x88x924 cm2/Vxc2x7s or more under an electric field of from 104 to 106 V/cm. Specific examples of the hole transporting zone include a hole injecting layer, a hole transporting layer and the like, and a light emitting layer may be included in some cases.
In the invention, the compound represented by the general formulae (I), (II) and (II)xe2x80x2 has a phenylenediamine skeleton and has a small ionization potential, and furthermore an excellent hole mobility can be ensured by the central skeleton shown by X and Y. In the invention, because the phenylenediamine derivative suitable as a hole injecting and transporting material is contained in the hole transporting zone, the driving voltage of the organic EL device can be decreased, and the increase of the driving voltage due to continuous driving can be suppressed.
Furthermore, in the invention, a light emitting layer containing a charge injection auxiliary is necessarily used.
The charge injection auxiliary herein means a compound having an ionization energy that is smaller than-the ionization energy of the main material forming the light emitting layer, and preferably a material assisting hole injection by adding in an amount of from 0.1 to 20 wt % into the light emitting layer. By the addition of the charge injection auxiliary, the organic EL device of the invention can lower the driving voltage and also can stabilize the driving voltage. The use of the phenylenediamine and the addition of the charge injection auxiliary into the light emitting layer bring about the effect that has not been obtained.
As the charge injection auxiliary, a compound, such as a styrylamine derivative, a distyrylarylene derivative, a tristyrylarylene derivative, a diamine derivative and the like, can be used, and particularly, a compound having an ionization energy of from 5.0 to 5.6 eV is preferred. The charge injection auxiliary may emit light in response to the recombination of a hole and an electron occurring in the light emitting layer, or may exhibit the effect of assisting charge injection without emission of light.
The hole transporting zone preferably has a hole injection layer containing the phenylenediamine derivative represented by the general formula (I), the general formula (II) or the general formula (II)xe2x80x2.
Alternatively, the hole transporting zone may have a hole transporting layer containing the phenylenediamine derivative represented by the general formula (I), the general formula (II) or the general formula (II)xe2x80x2.
In the foregoing, at least one of Ar1 to Ar6 in the general formula (I) is preferably a condensed aromatic ring having from 10 to 24 nucleus carbon atoms. According to this, the low voltage driving can be realized, and further the life time of the device can be prolonged.
On the other hand, the compound of the invention is a phenylenediamine derivative represented by the general formula (III). 
(Ar13 to Ar18 represent an aryl group having from 6 to 24 nucleus carbon atoms, which may be substituted with a hydrogen atom, an alkyl or an alkoxy group having from 1 to 6 carbon atoms, an aryl group having from 6 to 24 nucleus carbon atoms, or a styryl group. X represents a linking group, which is a single bond, arylene having from 6 to 24 nucleus carbon atoms, alkylene having from 1 to 6 carbon atoms, diphenylmethylene, an ether bond, a thioether bond, a substituted or unsubstituted vinyl bond, or an aromatic heterocyclic ring. R7 and R8 represent an alkyl group having from 1 to 6 carbon atom(s), an alkoxy group, or a hydrogen atom, which may be bonded to each other to form a substituted or unsubstituted saturated 5-membered ring or a saturated 6-membered ring.)
Furthermore, the compound of the invention is a phenylenediamine derivative represented by the general formula (IV). 
(Ar19 to Ar24 represent an aryl group having from 6 to 24 nucleus carbon atoms, which may be substituted with a hydrogen atom, an alkyl or an alkoxy group having from 1 to 6 carbon atom(s), an aryl group having from 6 to 24 nucleus carbon atoms, or a styryl group. Y represents a linking group, which is a single bond, arylene having from 6 to 24 nucleus carbon atoms, alkylene having from 1 to 6 carbon atom(s), diphenylmethylene, an ether bond, a thioether bond, an aromatic heterocyclic ring, or a substituted or unsubstituted vinyl bond. R9 and R10 represent an alkyl group having from 1 to 6 carbon atoms, an alkoxy group, or a hydrogen atom, which may be bonded to each other to form a substituted or unsubstituted saturated 5-membered ring or a saturated 6-membered ring.)
Alternatively, the compound of the invention is a phenylenediamine derivative represented by the general formula (V). 
(Ar25 to Ar30 represent an aryl group having from 6 to 24 nucleus carbon atoms, which may be substituted with a hydrogen atom, an alkyl or an alkoxy group having from 1 to 6 carbon atom(s), an aryl group having from 6 to 24 nucleus carbon atoms, or a styryl group. Y represents a linking group, which is a single bond, arylene having from 6 to 24 nucleus carbon atoms, alkylene having from 1 to 6 carbon atom(s), diphenylmethylene, an ether bond, a thioether bond, an aromatic heterocyclic ring, or a substituted or unsubstituted vinyl bond. R11 and R12 represent an alkyl group having from 1 to 6 carbon atoms, an alkoxy group, or a hydrogen atom, which may be bonded to each other to form a substituted or unsubstituted saturated 5-membered ring or a saturated 6-membered ring.)